56 GREAT NORTHERN DIVER OR LOON. 
Young in winter. Plate CCCVI. Fig. 2. 
Bill pale yellowish-green, the ridge and tip of the upper mandible 
dusky. Iris brown. Feet dusky externally, pale yellowish flesh-co- 
lour internally, webs dusky, but yellow in the middle. Claws yellow- 
ish-brown. All the upper parts are of a uniform dark greyish-brown, 
each feather margined with lighter, the lower parts white; the sides 
of the neck at the lower part whitish, streaked with dusky ; the sides 
dusky, without spots. 
Towards spring the eye assumes a redder tint, and the plumage of 
the upper parts gradually becomes spotted with white ; and when the 
moult is completed about the end of summer, the plumage is as in the 
adult, although the tints are improved at each successive moult for se- 
veral years. 
A fine male killed at Boston, 34 inches in length, with an alar ex- 
tent of 56, presents the following characters. There is a general layer 
of subcutaneous adipose tissue, and the skin is very tenacious. The 
external aperture of the ear roundish, very small, having a diameter 
of only 2 lines. The tongue is 2 inches 1 line in length, fleshy, as 
high as broad, slightly concave and longitudinally grooved above, ta- 
pering to a horny point. On the palate are 6 rows of papillae; the 
posterior aperture of the nares is linear 23 inches in length. The 
aperture of the glottis is } an inch long, with numerous papille along its 
sides and behind. The pharynx is extremely dilatable, as is the 
cesophagus, which is 17 inches long, passes along the right side of the 
neck, together with the trachea, and when distended has an average 
diameter of 23 inches, but on entering the thorax contracts to 12. 
The structure of the cesophagus in birds may be very conveniently 
examined in this species, the different layers being remarkably deve- 
loped in it. Properly speaking, it has only two coats,—the outer mus- 
cular, its external layer composed of transverse or circular fibres, the 
internal of equally distinct longitudinal fibres, which are not straight, 
but irregularly undulated. The inner, or mucous coat, when con- 
tracted falls into longitudinal plaits. The proventriculus is 23 inches 
long, the glandules large, roundish, simple, and disposed in a conti- 
nuous belt. Over this part, the transverse muscular fibres are remark- 
ably developed. The right lobe of the liver is 53 inches long, the 
left lobe 54. The heart is very large, of a broadly conical form, 3 
